The present invention relates to an adaptive cruise control system which is mounted in a vehicle to control the operation of the vehicle associated with cruising.
An adaptive cruise control (which will be referred to as ACC or ACC control, hereinafter) system can realize a function of following up a preceding vehicle. Though the preceding vehicle follow-up function of the related art ACC system is intended to be used in expressways, the system is spreading its application to ordinary roads whose terrains vary more largely than the expressway.
However, the ACC system confirms a headway distance with use of a millimeter-wave radar, a laser radar, a stereo camera, etc. Thus when the vehicle comes to a site point where road inclination or curvature is changed, departure of the preceding vehicle from a laser or camera detection range causes the system not to able to detect the preceding vehicle. That is, there occurs a so-called ‘lost condition or state’ that the system fails to detect the preceding vehicle or the system loses the preceding vehicle. For example, when the vehicle runs under the ACC control such a terrain that the vehicle runs on an ascending slope immediately followed by a descending slope, the preceding vehicle is hidden by the top of the road and the ACC system temporarily loses the preceding vehicle. In this case, the ACC system of the vehicle (to be controlled by the ACC system, which vehicle will be referred to merely ‘the controlled vehicle’, hereinafter) determines the absence of the preceding vehicle, and the vehicle runs at a set speed selected by the driver as a target speed. Thus, when the target speed is higher than a speed under the ACC control, the controlled vehicle is accelerated. However, the controlled vehicle comes nearly to a preceding-vehicle lost site point, the preceding vehicle suddenly appears. This causes the vehicle to be returned to ACC control, thus abruptly decelerating the vehicle.
A related art technique is known that, after an ACC system lost a preceding vehicle, a target speed is set at a current vehicle speed, so that, when the controlled vehicle subsequently comes to a preceding-vehicle lost site point (where the preceding vehicle departs from a headway distance detection range of the controlled vehicle), based on a change in a steering angle or in a road inclination the ACC system determines temporary lost condition of the preceding vehicle is caused by the terrain (see JP-A-7-232573).